Degradation of organic pollutants by ultraviolet/ozone in high salinity condition: Non-radical pathway dominated by singlet oxygen

Abstract

In this work, the combined ultraviolet ozone process (UV/O₃) was applied for organic contaminant (Reactive Blue K-GL, RB) degradation in high salinity. The degradation rates of RB in both O₃ and UV/O₃ systems were enhanced by NaCl (the k increased from 0.080 to 0.116 to 0.132 and 0.267 min^-1 respectively), while mineralization rate varied at different salt conditions. In addition, UV irradiation promoted the degradation efficiency of RB with the presence of salt. Singlet oxygen (¹O₂) was the primary active species in the UV/O₃ system. The quenching experiments and signal intensity of ¹O₂ corresponded well to the mineralization of RB. Under conditions of high salinity and high pH, O₃ has high mass transfer coefficient (k_La, 3.303 min^-1) and self-decomposition (k_d, 0.600 min^-1), which further promoted the formation of ¹O₂ for mineralization of RB. Furthermore, UV/O₃ system was efficient in real textile wastewater treatment (COD_Cr removal rate 91.7% and decolorization rate 98.7%).

Keywords: Non-radical oxidation; Ozone; Ozone mass transfer; Saline wastewater; UV irradiation.